Dosage-dispensing devices find application in particular in dispensing small quantities, for example of toxic substances, with high precision into small target containers. Frequently, such recipient containers are placed on a balance in order to weigh the substance delivered out of the dosage-dispensing device, so that the substance can subsequently be further processed according to given specifications.
The substance to be dispensed is contained for example in a source container which has a connection to the dispensing head and, to perform the dispensing function, forms a unit with the dispensing head, said unit being referred to as the dosage-dispensing device. It is desirable to deliver the substance to the outside through a small outlet opening of the dosage-dispensing device, so that the substance can be filled in a targeted stream also into a container with an opening of narrow cross-section.
Dosage-dispensing devices for dry and/or powdery substances of a pourable consistency belong to the known state of the art and are in current use. For example in U.S. Pat. No. 5,145,009 A, a device for dispensing measured doses is described which consists of a dispensing container with a closable outlet at its underside. As a closure device for the outlet, a cone-shaped valve body is used whose diameter decreases in the upward direction, which can be moved vertically downward in order to open an outlet opening. This valve body rotates when it is in its open position and is equipped with means to move the substance in the direction of the outlet opening.
The device of the foregoing description is not well suited for dispensing substances into containers with an opening of narrow cross-section. The upward-narrowing shape of the valve body as well as the rotary movement of the latter impart a radial, horizontal velocity component to the particles of the outflowing material leaving the outlet opening and therefore cause a dispersion of the material stream which can spread beyond even a relatively large-diameter opening of a recipient container that is to be filled.
A method and a device for the delivery of an extremely small sample of a substance in powder- or paste form, for example for atomic absorption spectroscopy, is disclosed in U.S. Pat. No. 4,905,525 A. In a reservoir container with an outlet opening at the end of a tubular channel, a tamping piston reaches from above into the sample material inside the container. By pushing the tamping piston into the sample material so that the latter is compacted in the area above the tubular channel, a small quantity is pressed through the tubular channel and discharged from the outlet opening. In a special embodiment, the container is configured in the shape of a funnel towards the outlet opening, and the tamping piston is arranged at an oblique angle to the outlet opening.
In DE 198 41 478 A1, a dosage-dispensing device is described which serves to fill packages of viscous, pasty, powdery or granular products, with a dosage-dispensing container whose profile, in the operating position of the dosage-dispensing device, narrows down towards the bottom end, where an outlet opening is arranged. A hollow shaft arranged at the center carries scraping tools. The dosage-dispensing device is equipped with a dispensing valve which includes a valve rod that is arranged in the hollow shaft and is movable up and down inside the latter in translatory motion. At the bottom end of the valve rod, a valve head is arranged which is conically tapered, its width decreasing in the upward direction, so that the fill quantity of material delivered into the package can be regulated and the outlet opening can be closed from above. In some of the afore-described embodiments, the dispensing valve is also designed to be rotatable.
In a dosage-dispensing device according to DE 198 41 478 A1 or according to U.S. Pat. No. 5,145,009 A, the dosage quantity to be dispensed from the container cannot be arbitrarily small. Since the outlet opening is ring-shaped, the minimum width of the ring gap needed to dispense a substance must be at least equal to the dimension of a smallest material unit of the substance—for example a powder particle—and furthermore, several substance units can pass through the ring gap simultaneously. There is also the risk that, depending on the properties of the substance, part of the gap can become clogged. This can occur particularly towards the end of a dosage-dispensing process, when the outflow rate is to be slowed down by reducing the width of the ring gap, because the ratio between the width and the length of the gap becomes more and more unfavorable.
In EP 1 931 950 B1, a dosage-dispensing device with a delivery- and closure element is shown, wherein the aforementioned drawbacks have been overcome so that measured doses of minute quantities of powdery or pasty substances can be dispensed into a container. In addition, a conveyor tool is proposed in EP 1 931 952 B1 which is supported and guided with translatory mobility relative to the delivery- and closure element along the central longitudinal axis of the latter, so that in the operating state of the dosage-dispensing device, the conveyor tool is always in loose contact with the rim of the housing that surrounds the outlet opening. The purpose is to ensure that even when the passage opening is reduced to a minimum, there is always enough of the dosage material being brought to the passage opening. The aim is to make it possible, through the combined action of the conveyor tool and the delivery- and closure element, to dispense measured doses of powders that have a strong tendency to coagulate, or powders with charged particles, or pastes, through an arrangement in which these substances are loosened up, conveyed to the passage opening in a controlled manner, and wiped away from the rim of the outlet opening.
A dosage-dispensing device with a delivery- and closure element in accordance with EP 1 931 950 B1 and EP 1 931 952 B1 was found to be at a disadvantage if the objective is to dispense larger fill quantities with a consistent degree of accuracy, because the discharge rate is limited by the cross-sectional area of the delivery- and closure element. Attempting to simply increase the cross-section of the delivery- and closure element can have the result, that the powdery- or pasty substance is not being moved at a sufficient feed rate. This has a negative effect on a steady fill rate or on the ability to meet the accuracy tolerance for the targeted fill quantity.